Option 2)
If a card is transferred from one account to another during a single season, it cannot be used in ranked play. This prevents a single card being used to boost multiple accounts to the stratospheric bounds of Champion I.
In addition, it stops the ability to farm cards easily and freely.
I would say this option is best imo, annoying for genuine trades but its a small wait to take for the stability of the game. Option 1 would work well but make it far to expensive for many people.